How to find documents by a field from a ref?-CodePudding

Suppose I have the following two schemas:

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const schemaA = new Schema({
    tag: [
        {
            type: mongoose.Schema.Types.ObjectId,
            ref: 'schemaB',
        },
    ],
});

module.exports = SchemaA = mongoose.model('schemaA', schemaA);

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const schemaB = new Schema({
    name: {
        type: String,
    }
});

module.exports = SchemaB = mongoose.model('schemaB', schemaB);

How can I find all documents in SchemaA that have their tag field match the name of SchemaB?

I know that if I had the _id of SchemaB, I'd be able to do this as,

const schemaBId = 'some-_id-string'
const docs = await SchemaA.find({ tag: schemaBId })

But how can I do this, if I only have the name value?

CodePudding user response：

You can try using mongoose populate() function it might help you achieve exactly what you want. Here is the populate docs for quick reference.

CodePudding user response：

first use lookup to get data of ModelB and then put these data as t after that make query with match to find where name of ModelB is test

ModelA.aggregate([
    {
        $lookup: {
            from: 'collectionB',
            localField: 'tag',
            foreignField: '_id',
            as: 't',
        },
    },
    {
        $match: { 't.name': 'test' },
    },
]);